1. Field of the Invention
This invention relates to a bioerodible ocular insert for dispensing drugs to the eye that has improved retention in the eye.
2. Description of the Prior Art
Ocular inserts represent a significant advance in the therapy of eye disease. Raher than periodically treating the eye as practiced in the prior art with medication in liquid or ointment form which is rapidly removed from the eye surface by tears, ocular inserts provide a useful sustained release of drug to the eye for a prolonged period of time. Bioerodible ocular inserts are described in Belgian Pat. No. 788,575 dated Sept. 29, 1972 (corresponds to German Offen. P2243986 published Mar. 29, 1973 and U.S. application Ser. No. 179,129 filed Sept. 9, 197l), U.S. Pat. No. 3,811,444 issued May 21, 1974, and U.S. application Ser. No. 544,808 filed Jan. 28, 1975, all assigned to the same assignee as this application. Said patents, publication, and applications are herein expressly incorporated by reference both to illustrate the background against which the present invention was made and to set out examples of the type of ocular insert to which the present invention applies.
Briefly, these ocular inserts act as drug dispensers, remaining in, and slowly releasing drug to the eye over prolonged periods of time. The inserts are fabricated of flexible polymeric materials that are biologically inert, non-allergenic, and bioerodible in the environment of the eye. They comprise a body having a size and shape adapted for insertion and wearing in either cul-de-sac. Once placed in either culde-sac, it remains in the eye, releasing drug until either:
1. it is removed, PA1 2. its supply of drug is exhausted, PA1 3. it erodes away, or PA1 4. it is expelled and lost from the ocular cavity.
Any of the first three fates for an ocular device are acceptable since their times of occurence are predictable. The patient will, or at least should, know that the drug is, or is not, being delivered to the eye. If the ocular device is removed, obviously, no drug is thereafter administered. If the drug supply is exhausted or the device has eroded (both events being tied to the stated life of the devices) no drug is thereafter delivered.
The fourth fate for an ocular device, expulsion, must be prevented during the prescribed therapy time. Such expulsion presented a statistically significant problem in the case of prior bioerodible ocular inserts. If involuntary expulsion occurs, the patient may not even know when expulsion has occurred, since ocular inserts are generally so comfortable that their presence or absence in the ocular cavity is not readily noted. Thus, it is possible that after expelling its ocular insert, an eye might go for seriously long periods without needed medication. This would negate one of the primary advantages of an ocular insert, which is controlled continuous medicating of the eye, and potentially, as a result of patient reliance on the ocular device coupled with a failure to check for the presence of the device, could lead to prolonged periods without medication.
It can therefore be seen that a discovery which would improve the eye's retention of ocular inserts and eliminate to any major extent the unpredictable expulsion or ejection of bioerodible ocular inserts from the ocular cavity would indeed be beneficial. The present invention does this.